Transient neurobiological responses to low-level blast during Swedish military special forces breacher training

Introduction Low-level blast (LLB) exposure is a recurring element of military breacher training, yet its biological and cognitive effects remain insufficiently understood. This study investigated the impact of real-world LLB exposure during scheduled breaching training in the Swedish Armed Forces. Methods 14 soldiers participated across two training weeks and underwent repeated assessments of blast exposure, neurocognitive performance and blood-based biomarkers of neurotrauma (tau, neurofilament light, neuron-specific enolase (NSE) and S100B). Blast overpressure was recorded using wearable sensors mounted on the head, chest and shoulder. Cognitive performance was assessed with the tablet-based Defense Automated Neurobehavioural Assessment test battery. Biomarker concentrations were analysed using Simoa and immunoassay platforms. Results Average blast exposure was low (mean peak 13–20 kPa (2–3 pounds per square inch (psi))), although considerable variability occurred depending on operational role and environmental conditions. All biomarkers showed significant fluctuations over time, with an initial increase following exposure. Except for NSE, biomarker levels declined towards baseline within days, suggesting transient physiological responses to LLB exposure. Cognitive results were inconclusive due to limited complete datasets; however, several reaction-time measures improved at follow-up, potentially reflecting training effects rather than blast-related changes. Conclusions The findings demonstrate measurable, but short-lived biomarker responses to realistic LLB exposure, with no clear evidence of cognitive impairment. Limitations include small sample size, uneven exposure levels and high dropout rates. Nevertheless, the study supports the feasibility of combining wearable blast sensors, fluid biomarkers and digital cognitive testing to evaluate blast-related neurobiological effects in operational training environments. The results also support recent guidelines suggesting that peak pressures below 4 psi represent a reasonably safe exposure level. While current exposure levels appear safe, further studies should examine cumulative effects, long-term trajectories and higher-exposure scenarios to refine safety guidelines and monitoring practices.